Preheat oven to 325º F.
Place cupcake liners in muffin tin. Spray lightly with cooking spray.
Add flour, sugar, cocoa, baking powder, baking soda, salt and espresso powder to a large bowl or the bowl of a stand mixer. Whisk through to combine or, using your paddle attachment, stir through flour mixture until combined well.
Add milk, vegetable oil, eggs, and vanilla to flour mixture and mix together on medium speed until well combined. Reduce speed and carefully add boiling water to the cake batter. Beat on high speed for about 1 minute to add air to the batter.
Evenly distribute cake batter. Each cupcake liner should be about ¾ths full.
Place in the oven and bake 12-15 minutes or until a toothpick inserted in the center comes out clean.
Remove from the oven and allow the cupcakes to cool completely.

Place softened butter into the bowl of a stand mixer that has been fitted with the paddle attachment. Turn the mixer on a medium setting and cream the butter until it is smooth and has lightened in color, about 3 minutes.
Add confectioner’s sugar, ½ a cup at a time. After each cup has been incorporated, turn the mixer onto the highest speed setting and for about 10 seconds to lighten the frosting.
Add vanilla and a pinch of salt and combine until well-incorporated.
Add milk, heavy cream or half-and-half until the frosting has reached the preferred consistency. For a firmer frosting, add more confectioner’s sugar, a ¼ cup at a time. For a softer frosting, add more milk or cream, a tablespoon at a time.

Once the cupcakes have completely cooled, spread or pipe the buttercream frosting onto each one and decorate with toppings of your choice or just leave ’em plain.